diff --git a/app/views/layouts/_matomo_tag.html.haml b/app/views/layouts/_matomo_tag.html.haml
index 85a4cf47dc..7b8bbe834b 100644
--- a/app/views/layouts/_matomo_tag.html.haml
+++ b/app/views/layouts/_matomo_tag.html.haml
@@ -1,7 +1,7 @@
 
 - if Spree::Config.matomo_tag_manager_url.present?
   :javascript
-    var _mtm = _mtm || [];
+    var _mtm = window._mtm = window._mtm || [];
     _mtm.push({'mtm.startTime': (new Date().getTime()), 'event': 'mtm.Start'});
     var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
     var u="#{Spree::Config.matomo_tag_manager_url}";